This is on my "Essential not quite horror but more brutal" movies list from a couple years ago. It's amazing more people don't do this... rip off foreign cinema or book, write an American version, get rich... ala Hunger Games

Where is this list of yours? If Oldboy (trilogy) isn't on it - I don't care about it anymore.
And Battle Royal was indeed a book before movie -- I own it but never finished it.